Vulcanization of rubber



Patented Jan. 12, 1954 VULCANIZATI-ON F RUBBER Edward L. Carr and George E. P. Smith, Jr., Akron, Ohio, assignors to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of ()hio No Drawing.

Original application March 17, 1951, Serial No. 216,252.

Divided and this application March 31, 1952, Serial No. 281,661

Thisinvention relates to the vulcanization of rubber, and relates especially to a new class of chemical compounds which are valuable accelerators of the vulcanization of rubber 01' rubher-like substances.

This application is a division of application Serial No. 216,252, filed March 17, 1951, which is a continuation-in-part of application Serial No. 39,380, filed July 17, 1948, now abandoned; the latter application was a continuation-in-part of application Serial No. 488,555, filed May 26, 1943, now Patent No. 2,445,722.

An object of the present invention is to provide a new class of improved rubber vulcanization accelerators of the delayed-action, nonscorching type.

Another object is to provide a method of vulcanizing rubber, whereby scorching or pre-vulcanization during processing of the rubber compound is prevented, but extremely rapid vulcanization is obtained at customary vulcanizing temperatures.

Another object is to provide improved rubber compositions possessing the ability to vulcanize extremely rapidly at ordinary vulcanizing temperatures, but free from any tendency to set-up or pre-vulcanize at rubber processing temperatures.

A further object is to provide vulcanized rub- ,ber of improved quality, possessing the characteristics of high modulus and tensile, low hysteresis and a high inherent resistance to deterioration by flexing or aging.

The above and further objects will be manifest in the description of the invention which follows.

It has been found that members of a new class of chemical compounds are very effective in accelerating the vulcanization of natural or synthetic rubber. The new compounds may be conveniently prepared by oxidizing a mixture of 2- mercaptothiazole and a primary amine. The preparative oxidation reaction may be effected by treating a mixture of the mercaptothiazole and an excess of the amine in an alkaline aqueous medium with one of the following oxidizing agents: chlorine, bromine, iodine, hypochlorous acid, hypobromous acid, hypoiodous acid, and

alkali metal and alkaline earth metal salts of said acids. The oxidation reaction is believed to comprise the direct action of the oxidizing agent on a mixture of the mercaptothiazole and one equivalent of the amine. The desired substances .produced by this oxidation reaction are 9 Claims. (01. 26079.5)

2 organic compounds containing nitrogen and sulfur.

The new class of chemical compounds possesses the following type formula:

wherein R is an alkyl radical or a cyclo-alkyl radical. Thus, the new compounds are derivatives of sulfenamide (HSNHz). Examples of alkyl and cyclo-alkyl radicals include methyl, ethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, decyl. lauryl, cyclohexyl, methylcyclohexyl, benzyl and similar radicals.

The Z-mercaptothiazole may be prepared from alpha-chloroacetaldehyde and ammonium dithiocarbamate in alcoholic or aqueous solution, in accordance with the following equation:

HO-N

means of an aqueous sodium hypochlorite solution or the like to produce the new class of sulfenamides in accordance with the following equation:

HCN

i /CSH RNHz o H- -s H-C-N CSNHR H20 HO-S Upon testing the sulfenamides as rubber vulcanization accelerators in the manner described in our Patent No. 2,445,722, they are found to be effective delayed-action accelerators, which are extremely active at normal vulcanizing temperatures of approximately 270-400 F., producing natural and synthetic rubber vulcanizates having high modulus and tensile characteristics and resistance to aging.

Example 1 An aqueous alkaline (sodium hydroxide) solution of 2-mercaptothiazole was mixed with an excess of cyclohexylamine over theaamount' -required by the last-preceding equation, and the mixture was stirred during theigraiduahadditien thereto of an aqueous solutiomcontaining about of iodine and about ioaer' otassmm iodide. The solid reaction product, N-cyclohexyl-Q-thiazole sulfenamide,

was separated andrecr'ystalli'zed' from petroleum ether. The purified product melted at 52-530.

and analyzed as" follows:

Calculated for C9H14S2N2 N, 13.08%; S, 29.9%

Found N, 13.07%; S, 29.7%

Example 2 1. In .a-similarflmanner isopropylamine was con- .densed with .2 -.mereaptothiazole .to produce N.-.-isopropy1-2-thiazo1e sulfenamide,

5E cs as a-liquidproduct. This product waspurified by isolation in .ethersolution, followed by thorough washing of the ether solution with water, drying this washed solution and then removing the ether therefrom by evaporation under a vacuum.

Example 3 .Primary secondary --amylamine (2 -pentylamine) was reacted with .z-mercaptothiazole' by .the methodof Example 1 toproduceN-sec-amyl- 2ethiazolesulfenamide,

This sulfenamide was a liquid, and was, purified "as was the product otExample 2.

.The .sulfenamides 0f Examples 1 and 3 -were .teste'd .-as rubber vulcanization accelerators by comparing them with Z-mercaptothiazole in the following rubber formula:

Samples of the three rubber composition, so Tformulated, were heated for and '30 minutes at "140 F. to determine whether or not they possessed any tendency to pre-vulcaniz'e'or set-up during processing operationspfior -to the usual vulcanizing step, and the following physical testing data were obtained:

Modulus of elasitipittyy in 'lleirlilsfle Sstgeggth p.js..a 6W I" Acceleiggri cure at I Elongation reak 15 min. 30 min. 15 min. 30 min.

2-mercaptothiazole 0 50 475 N-cyclohexyl-2-thiazole sulfen'amide. .e 0 50 0 126 A. N scc-amyl-2-thiazole sulfenamide 0 50 0 The last set "of data 'shows i that the 'sulfenamides of the invention impart higher physical properties to thejrubber after a heat treatment comparable to conventional rubber' vulcanization practice.

:The various members -of the 'new mass of :chemical compounds are equally effective delayed-action vulcanization accelerators in rubber 'treald compounds, latex compoundsor other con- 've'ntion'al itypes of vulcanizable compounds ef rubber, reclaimed rubber, or synthetic rubber. and=wconsistently produce rapid-curing composi- -tions, "which in tne" vulcanized state possess unusually high modulus, tensile and abrasionresisting properties. The various synthetic rubbers vulcanizable :by heating with sulfur are herein considered equivalentto rubber, examples being butadiene polymers, isoprene polymers and various interpolymersJofconjugated diolefins' and vinyl compounds, such as GR=S copol'ymer of :butadiene ands styr'ene) and GR-A ('copolymer of butadiene and acrylonitrile) Although sulfur has hereinabove been mentioneda's the. preferred vulcanizing agent, other :known "vulcanizing agents susceptible-to acceleration (such astetramethylthiuram disulfide, polysulfidesof phenols and cresols, diethyl .xanthogen disulfi-de, and other vulcaniz'ingagents ofjthe sulfu'rdonor type). are contemplated.

'The preferred classo'f sulfenarni'de derivatives may 'beiprepared by other "methods than those fmentioned above. "For example, 'a mixture of 2-mercaptothiazole "and a "primary "amine may be oxidized by hydrogenperoxide or "other oxidizing agent. The invention is "not limited to derivatives prepared inaccordance withanypar- 'ticular method, but includes -the preferred class of compounds, however .they may "have -been formed.

In addition to the above-enumerated desir'able properties imparted I by the: new :acceleratorswo rubber compositions, it will be noted that the vulcanized compositions also are highly efficient, having low hysteresis characteristics. When compared to conventionally accelerated vulcanized rubber compositions, the new compositions are found to be unusually resistant to deterioration upon flexing or aging.

Conventional accelerator activators may be employed to an advantage with the new class of accelerators when extremely rapid vulcanization is desired, especially at lower temperatures. Also, the new accelerators may be used in combination with other accelerators, such as a guanidine (e. g., diphenyl guanidine) or a conventional mercaptothiazole derivative (e. g., mercaptobenezothiazole or 2,2'-dithiobis-benzothia zole) or a dithiocarbamate-type accelerator (such as tetramethylthiuram disulfide, or the zinc salts of dimethylor diethyl-dithiocarbamic acids), in order to produce rubber compositions having especially rapid or specific vulcanizing properties. Although the new accelerators are usually employed in the proportion of 0.5 to 2.0 parts per 100 parts of rubber, they may be utilized in the range of 0.1 to parts per 100 parts of rubber.

What is claimed is:

1. The method of vulcanizing rubber which includes heating rubber and sulfur in the presence of a small amount of N-cyclohexyl-Z-thiazole sulfenamide,

2. A vulcanizable rubber composition including rubber, sulfur and a small amount of N-cyclohexyl-2-thiazole sulfenamide.

3. A vulcanized rubber product prepared by heating rubber and sulfur in the presence of a small amount of N-cyclohexyl-Z-thiazole sulfenamide.

4. The method of vulcanizing rubber which includes heating rubber and sulfur in the presence of a small amount of N-sec-amyl-2-thiazole sulfenamide.

5. A vulcanizable rubber composition including rubber, sulfur and a small amount of N-sec-amyl- 2-thiazole sulfenamide.

6. A vulcanized rubber product prepared by heating rubber and sulfur in the presence of a small amount of N-sec-amyl-Z-thiazole sulfenamide.

'7. The method of vulcanizing rubber which includes heating rubber and sulfur in the presence of a small amount of a substance selected from the group consisting of N-cyclohexyl-Z-thiazole sulfenamide and N-sec-amyl-Z-thiazole sulfer1- amide.

8. A vulcanizable rubber composition including rubber, sulfur and a small amount of a substance selected from the group consisting of N-cyclohexyl2-thiazole sulfenamide and N -sec-amyl-2- thiazole sulfenamide.

9. A vulcanized rubber product prepared by heating rubber and sulfur in the presence of a small amount of a substance selected from the group consisting of N-cyclohexyl-Z-thiazole sulfenamide and lNsec-amyl-2-thiazole sulfenamide.

EDWARD L. CARR. GECRGE E. P. SMITH, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 19,286 Zaucker et al Aug. 21, 1934 2,419,283 Paul et al Apr. 22, 1947 2,445,722 Carr et a1 July 20, 1948 FOREIGN PATENTS Number Country Date 593,748 Great Britain Oct. 24, 1947 

7. THE METHOD OF VULCANIZING RUBBER WHICH INCLUDES HEATING RUBBER AND SULFUR IN THE PRESENCE OF A SMALL AMOUNT OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF N-CYCLOHEXYL-2-THIAZOLE SULFENAMIDE AND N-SEC-AMYL-2-THIAZOLE SULFENAMIDE 